Communication device

ABSTRACT

A communication device which transmits/receives data to/from a host device connected thereto via a bus having a signal line and a power line. A communication controller which is always supplied with power as long as a bus is connected thereto and a MCU are so arranged as to use different power, and only supply of power to the MCU is interrupted when a connected host device comes into stand-by state. In case the connected host device resumes from the stand-by state, the communication controller responds to communication from the host device until the MCU resumes control of data transmission/reception with the host device.

This Application claims priority to PCT Application PCT/JP02/11734,filed on Nov. 11, 2002.

TECHNICAL FIELD

The present invention relates to a communication device which receivespower via a bus such as the USB (Universal Serial Bus), and performsdesired operations with a host device connected thereto.

This application claims priority of Japanese Patent Application No.2001-367859, filed on Nov. 30, 2001 in Japan, the entirety of which isincorporated by reference herein.

BACKGROUND ART

As a bus for connecting an electronic device such as a personal computerto peripheral devices, there is known the USB (Universal Serial Bus)bus.

The bus, which is represented by the USB bus, is a serial transmissionbus comprising a power line for supplying power to an electronic deviceconnected thereto and a transmission line for transmitting/receivingdata. The bus can employ unconstrained connection configuration such asthe daisy chain and node branch, and can transmit data preferentially.Furthermore, employing the bus, cables can be attached or detached withan electronic device being supplied with power, and a network under thebus can be automatically restructured at the time when nodes are addedor removed. Thus, the bus, which is represented by the USB bus, is usedas an interface of an electronic device such as a VTR, a video camera, acolor scanner, or a digital still camera which sends and receivesmultimedia data.

Respective electronic devices using the bus as an interface cannotfreely consume arbitrary power, and are subject to power consumptionstipulated based on specification given in advance. Especially, whenthere is no bus activity on the USB bus for more than a predeterminedperiod of time due to suspension, etc. of an electronic device (referredto as stand-by state, hereinafter), power which can be consumed by theelectronic device using the bus is restricted to 500 μA at most. So, inorder to fulfill stipulated power consumption in the stand-by state, anelectronic device is caused to transition into low power consumptionmode in which power consumption of the electronic device is suppressedto the least.

As semiconductor processes are caused to be refined recently, eventhough an electronic device transitions into low power consumption mode,leak current increases in a semiconductor circuit of the electronicdevice, which cannot fulfill stipulated power consumption in thestand-by state. Especially, in a ASIC having a large-scale MCU (MemoryControl Unit) or MPU (Micro Processing Unit) built therein, powerconsumption may increase to approximately 1 mA even in low powerconsumption mode.

On the other hand, in case power of an electronic device is shut down inthe stand-by state, when resuming from the stand-by state, since a longtime is required for rise time of a power source and for initializationtime of a semiconductor circuit, there is raised a problem that theelectronic device is judged to be disconnected from the bus by aconnected external device.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has an object to provide a newcommunication device which can overcome the above-mentioned drawbacks ofthe prior art.

The present invention has another object to provide a communicationdevice which can fulfill stipulated power consumption in the stand-bystate, and can always respond to communication from an external devicewhen resuming from the stand-by state.

The above object can be attained by providing a communication devicewhich transmits/receives data to/from a host device connected theretovia a bus having a signal line and a power line, comprisingcommunication control means which can always respond to communicationfrom the host device, the communication control means being alwayssupplied with power as long as at least the bus is connected thereto,communication function means for controlling data transmission/receptionwith the host device through the communication control means, thecommunication function means working under power supplied via at leastthe bus, and power supply control means for controlling supply of powerto the communication function means, wherein, in case the host devicetransits into stand-by state, the power supply control means interruptssupply of power to the communication function means.

According to the communication device, the communication control meanswhich is always supplied with power as long as the bus is connectedthereto and the communication function means which may come into thestate in which supply of power is interrupted are separated, and onlysupply of power to the communication function means is interrupted whenthe connected host device comes into the stand-by state.

These objects and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram showing system configuration employing thecommunication device according to the present invention.

FIG. 2 shows a block diagram showing internal configuration of thecommunication device according to the present invention.

FIG. 3 shows a flow chart showing the operation of the communicationdevice according to the present invention.

FIG. 4 shows a block diagram showing internal configuration of thecommunication device according to the present invention, in which an MCUunit and a communication controller unit are arranged on the same LSI.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will further be described below concerning thebest modes with reference to the accompanying drawings.

The present invention can be employed in a communication device 1connected to a host device 2, as shown in FIG. 1. The communicationdevice 1 and the host device 2 are connected to each other via a bus 3.The bus 3 is used as an interface of an electronic device such as a VTR,a video camera, a color scanner, or a digital still camera which sendsand receives multimedia data. The bus 3 can use cables and connectors oflow cost by employing high speed data transfer, real time data transfer,and serial bus, which leads to reduction in system cost.

As the connection manner of the bus 3, which is represented by the USBbus, two kinds of methods or the “daisy chain” and “node branch” areemployed. Employing the bus 3, cables can be attached or detached withthe communication device 1 and the host device 2 being supplied withpower, and a network under the bus 3 can be automatically restructuredat the time when nodes are added or removed.

The communication device 1 shown in FIG. 1 employs the USB busconnection, and is connected to the host device 2 such as a personalcomputer which also conforms to the USB standard.

The communication device 1 is supplied with power via the bus 3. In casecommercial AC power can be obtained, the communication device 1 may besupplied with the commercial AC power using an AC adapter 4. Also, thecommunication device 1 may be supplied with power from a battery.

The communication device 1 includes a switch 11, a main power source 12,a sub power source 13, an MCU (Memory Control Unit) 14, a submicrocomputer 15, an MCU (Memory Control Unit) bus 16, a bus buffer 17,and a communication controller 18, as shown in FIG. 2.

The switch 11 may be a relay which mechanically works, and are connectedto the bus 3 and to the AC adapter 4. The switch 11 switches either tothe bus 3 side or to the AC adapter 4 side, and supplies either power tothe communication device 1. When detecting power supplied via the bus 3,the switch 11 automatically switches to the bus 3 side.

The main power source 12 has its ON/OFF controlled by the submicrocomputer 15 connected thereto, and supplies power from the switch11 to the MCU 14.

The sub power source 13 supplies power from the switch 11 to the submicrocomputer 15 and to the communication controller 18. The sub powersource 13 differs from the main power source 12 in that power is alwayssupplied thereto as long as the bus 3 and the AC adapter 4 or thebattery are connected to the communication device 1.

The MCU 14 works under power supplied from the main power source 12.Being connected only to the main power source 12 which may be set to beOFF, the MCU 14 may come into suspended state due to interruption ofsupply of power. The MCU 14 writes/reads out data to/from the bus buffer17 through the MCU bus 16. Since the communication controller 18sends/receives data to/from the bus buffer 17, the MCU 14 cansend/receive data to/from the communication controller 18. Furthermore,the MCU 14 controls data communication with the host device 2 throughthe communication controller 18.

The sub microcomputer 15 works under power supplied from the sub powersource 13. The sub microcomputer 15 is notified of the state of the hostdevice 2 from the communication controller 18, and controls ON/OFF ofthe main power source 12 based on the state. Furthermore, when the bus 3is connected to the communication device 1, the sub microcomputer 15notifies the MCU 14 of this matter.

The communication controller 18 is connected to the bus buffer 17, andsends/receives data to/from the bus buffer 17. The communicationcontroller 18 is connected to the host device 2, and detects the stateof the host device 2 minutely. Furthermore, being supplied with powerfrom the sub power source 13 which can always supply power, thecommunication controller 18 never comes into suspended state and canalways respond to communication from the host device 2, as is differentfrom the case of the MCU 14.

The operation of the communication device 1 according to the presentinvention will be explained with reference to a flow chart shown in FIG.3.

When the host device 2 comes into and remains in suspended state formore than a predetermined period of time due to suspension, etc., thatis, comes into the stand-by state (step S21), the communicationcontroller 18 detects this state in step S22.

Then in step S23, the communication controller 18 notifies the submicrocomputer 15 that the host device 2 comes into the stand-by state,and fixes the output of the bus buffer 17. Thus, the communicationcontroller 18 can make all accesses from the MCU 14 through the MCU bus16 invalid, and when the power of the MCU 14 is set to be OFF afterward,malfunction of the communication controller 18 due to indefinite data onthe MCU bus 16 can be prevented.

Then in step S24, the sub microcomputer 15 which is notified that thehost device 2 comes into the stand-by state from the communicationcontroller 18 sets the main power source 12 to be OFF. Thus, supply ofpower to the MCU 14, whose power consumption is large in the stand-bystate, is interrupted, which can reduce the whole power consumption ofthe communication device 1, thereby fulfilling stipulated powerconsumption in the stand-by state. At this time, the communicationcontroller 18 similarly comes into the stand-by state (step S25).

On the other hand, when the host device 2 resumes from the stand-bystate in step S31, then in step S32, the communication controller 18detects this state. In case of the USB, this is the “resume” state.

Then in step S33, the communication controller 18 notifies the submicrocomputer 15 that the host device 2 resumes from the stand-by state.The sub microcomputer 15 which is notified of this state from thecommunication controller 18 sets the main power source 12 to be ON, instep S34. Thus, power is resupplied to the MCU 14 which is not suppliedwith power during the stand-by state. Then, the MCU 14 which is suppliedwith power is activated (step S35).

Even though the MCU 14 is activated in step S35, in case a long time isrequired until the main power source 12 is completely activated andinitialization of the MCU 14 is completed, or until the MCU 14 resumescontrol of data transmission/reception with the host device 2, thecommunication controller 18 continuously notifies the host device 2 thatthe MCU 14 is not ready to work (step S36). Thus, the host device 2 doesnot judge that the bus 3 is disconnected.

The present invention is not restricted to above-described embodiment.For example, this invention is applicable to a communication device 5 inwhich an MCU and a communication controller are arranged on the sameLSI, as shown in FIG. 4. In the communication device 5 shown in FIG. 4,parts or components similar to those of the communication device 1 areindicated with the same reference numerals, and detailed explanation ofwhich will be omitted.

The communication device 5 includes a switch 11, a main power source 12,a sub power source 13, a sub microcomputer 15, and an LSI 19. The LSI 19has at least an MCU unit 19 a and a communication controller unit 19 bintegrated therein.

The MCU unit 19 a is supplied with power from only the main power source12. Being connected to the main power source 12 which may be set to beOFF, the MCU unit 19 a may come into suspended state due to interruptionof supply of power. The MCU unit 19 a controls data communication withthe host device 2 through the communication controller unit 19 b.

The communication controller unit 19 b is supplied with power from thesub power source 13. Being supplied with power from the sub power source13 which can always supply power, the communication controller unit 19 bnever come into suspended state and can always respond to communicationfrom the host device 2, as is different from the case of the MCU unit 19a.

The LSI 19 operates two portions, that is, components including the MCUunit 19 a and the communication controller unit 19 b, by using differentpower. Since the MCU unit 19 a which may come into suspended state dueto interruption of supply of power and the communication controller unit19 b which is always supplied with power are arranged on the LSI 19,different power is used in the LSI 19.

Furthermore, the LSI 19 has a terminal, not shown, for separating theMCU unit 19 a and the communication controller unit 19 b so as toprevent change of state in the communication controller unit 19 b whichoccurs when the MCU unit 19 a comes into suspended state due tointerruption of supply of power.

The operation of the communication device 5 will be explained.

When the host device 2 comes into the stand-by state, the communicationcontroller unit 19 b detects this state. Then, the communicationcontroller unit 19 b notifies the sub microcomputer 15 that the hostdevice 2 comes into the stand-by state, and make all accesses through anMCU bus, not shown, invalid. Thus, when the power of the MCU unit 19 ais set to be OFF afterward, malfunction such as that the MCU unit 19 awrites indefinite data to a register of the communication controllerunit 19 b can be prevented.

Then, the sub microcomputer 15 which is notified that the host device 2comes into the stand-by state sets the main power source 12 to be OFF.Thus, supply of power to the MCU unit 19 a, whose power consumption islarge in the stand-by state, is interrupted, which can reduce the wholepower consumption of the communication device 5. At this time, thecommunication controller unit 19 b similarly comes into the stand-bystate.

On the other hand, when the host device 2 resumes from the stand-bystate, the communication controller unit 19 b detects this state. Then,the communication controller unit 19 b notifies the sub microcomputer 15that the host device 2 resumes from the stand-by state, and the submicrocomputer 15 which is notified of this state sets the main powersource 12 to be ON. Thus, power is resupplied to the MCU unit 19 a whichis not supplied with power during the stand-by state.

Similarly, in case a long time is required for activation of the mainpower source 12 and for initialization of the MCU unit 19 a, thecommunication controller unit 19 b continuously notifies the host device2 that the MCU unit 19 a is not ready to work. Even though the mainpower source 12 is set to be OFF in the stand-by state, being alwayssupplied with power from the sub power source 13, the communicationcontroller unit 19 b can always respond to communication from the hostdevice 2.

As in the above, in the communication device employing the presentinvention, the communication controller which is always supplied withpower as long as the bus or commercial power source is connected theretoand the MCU are arranged on the same LSI or on different LSIs usingdifferent power, and only supply of power to the MCU is interrupted whenthe host device 2 comes into the stand-by state. Thus, the whole powerconsumption of the communication device can be reduced, therebyfulfilling stipulated power consumption in the stand-by state.

In the communication device 1 employing the present invention, when theconnected host device 2 is activated, the host device 2 is continuouslynotified that the MCU 14 is not ready to work until the main powersource 12 is completely activated and initialization of the MCU 14 iscompleted. Thus, the host device 2 does not judge that the bus 3 isdisconnected.

While the invention has been described in accordance with certainpreferred embodiments thereof illustrated in the accompanying drawingsand described in the above description in detail, it should beunderstood by those ordinarily skilled in the art that the invention isnot limited to the embodiments, but various modifications, alternativeconstructions or equivalents can be implemented without departing fromthe scope and spirit of the present invention as set forth and definedby the appended claims.

INDUSTRIAL APPLICABILITY

As in the above, in the communication device employing the presentinvention, the communication control means which is always supplied withpower as long as the bus is connected thereto and the communicationfunction means are so arranged as to use different power, and onlysupply of power to the communication function means is interrupted whenthe connected host device comes into the stand-by state. Thus, the wholepower consumption of the communication device can be reduced.

In the communication device employing the present invention, in case theconnected host device resumes from the stand-by state, the communicationcontrol means responds to communication from the host device until thecommunication function means resumes control of datatransmission/reception with the host device. Thus, the host device doesnot judge that the bus is disconnected.

1. A communication device for transmitting/receiving data to/from a hostdevice connected thereto via a bus having a signal line and a powerline, comprising: communication control means for responding tocommunication from the host device, the communication control meansbeing supplied with power while the bus is connected thereto;communication function means for controlling data transmission/receptionwith the host device through the communication control means, thecommunication function means working under power supplied via the bus,wherein said communication function means comprises a Memory ControlUnit (MCU); and power supply control means for controlling supply ofpower to the communication function means based on the state of the hostdevice notified from the communication control means; wherein, when thehost device transits into stand-by state, the power supply control meansinterrupts supply of power to the communication function means, and whencommunication control means detects a resumed active state of the hostdevice, the power supply control means resupplies power to thecommunication function means, and wherein the communication controlmeans notifies the host device of a ready status of the communicationfunction means.
 2. The communication device as set forth in claim 1,wherein, when the host device resumes from the stand-by state, thecommunication control means responds to communication from the hostdevice until the communication function means resumes control of datatransmission/reception with the host device.
 3. The communication deviceas set forth in claim 1, further comprising: selection means forselecting either power from power supplied via the bus or commercialpower as power to be supplied to the communication function means and tothe communication control means, wherein, when detecting the powersupplied via the bus, the selection means selects the power supplied viathe bus.
 4. The communication device as set forth in claim 1, whereinthe communication control means and the communication function means arearranged on the same LSI.